Senior staff at Goldman Sachs confronted Bloomberg after journalists at the media and financial data business told Goldman employees that they had been using the machines to keep tabs on the bank’s staff.

JP Morgan is also understood to have raised concerns about journalists accessing information about its staff to inform coverage of the “London Whale” scandal last year.

Writers were able to check on users to see how often they logged into their machines, what articles they were reading, and how often they used functions such as Bloomberg’s instant messaging service. “You can basically see how many times someone has looked up news stories or if they used their messaging functions. It made us think, 'Well, what else does [Bloomberg] have access to?’” the New York Post quoted one Goldman insider as saying.

It is understood Bloomberg staff were open about using the information. After the complaint, Bloomberg blocked access. “In light of [Goldman’s] concern as well as a general heightened sensitivity to data access, we decided to disable journalists’ access to this customer relationship information for all clients,” said a Bloomberg spokesman.

However, many traders remain worried about the potential security risk. The black boxes are common across the City and Wall Street, and are used to access share prices in real time and breaking financial news.